Focus state detection apparatus and optical instrument

ABSTRACT

A focus state detection apparatus has a sensor that senses light rays that pass through a lens subjected to focus detection and is composed of a plurality of photoelectric converter elements, a charge accumulation unit that accumulates pixel signals obtained by the sensor, a first accumulation controller that controls accumulation carried out by said charge accumulation unit at each area of a plurality of areas into which the sensor is divided, a second accumulation controller that combines at least a portion of the plurality of areas into a single combined area and controls accumulation carried out by said charge accumulation unit at such combined area, a first storage unit that stores each accumulated signal of each of the plurality of areas accumulation-controlled by the first accumulation controller, a second storage unit that stores the accumulated signal of the combined area accumulation-controlled by the second accumulation controller, and a defocus state detector that detects a defocus state of the area from the accumulated signal stored in either the first storage unit or the second storage unit.

RELATED APPLICATION INFORMATION

This application is a continuation of co-pending U.S. application Ser.No. 11/350,615 filed Feb. 8, 2006, which is incorporated herein byreference.

FIELD OF THE INVENTION

The present invention relates to a focus state detection apparatushaving a sensor that senses light rays that pass through a lenssubjected to focus detection and an optical instrument such as a camera,mobile phone or the like that is equipped with such focus statedetection apparatus.

BACKGROUND OF THE INVENTION

Conventionally, as a camera focus state detection apparatus, a so-calledphase difference focus detection method-type focus state detectionapparatus is known. In the phase difference focus detection method,light rays fro a subject that pass through different exit pupil areas ofan image sensing lens are focused on a pair of line sensors. Then, byobtaining the amount of shift of the relative positions of the pair ofsubject images obtained by photoelectric conversion of the subjectimages (hereinafter, this process is called “phase differencecomputation”), a subject defocus amount is detected and the imagesensing lens is driven based on that detected amount of defocus (forexample, Japanese Patent Application laid-Open No. 09-054242).

In addition, a multi-point focus detection apparatus that carries outfocus detection of a plurality of subjects is also known. In such anapparatus, the pair of line sensors is divided among a plurality ofareas, signal charge accumulation control is carried out for each area,and the pairs of subject images obtained by photoelectric conversion ateach of these areas are correlated (for example, Japanese PatentApplication Laid-Open No. 2003-215442).

In addition, in the focus state detection apparatus using the phasedifference focus detection method, a focus state detection apparatusthat can adjust the detectable defocus amount by changing the area ofthe pair of line sensors used for charge accumulation control and phasedifference computation is also known (for example, Japanese PatentApplication Laid-Open No. 63-172206; see FIG. 8).

The focus state detection apparatus disclosed in Japanese PatentApplication Laid-Open No. 63-172206 makes it possible to select anappropriate charge accumulation control area depending on the focusstate detection results and the maximum defocus amount of the imagesensing lens. However, where focus state detection does not function, itis necessary to change the charge accumulation control area and to redothe charge accumulation operation and the phase difference computationoperation, which lengthens the time required for focus state detection.

In addition, the focus state detection apparatus of Japanese PatentApplication Laid-Open No. 63-172206 can also be adapted to a multi-pointfocus detection apparatus that enables focus state detection of aplurality of subjects like the focus state detection apparatus ofJapanese Patent Application Laid-Open No. 2003-215442. As an example ofan instance in which such a focus state detection apparatus is created,charge accumulation control areas at three distance measurement points(focus state detection areas) are illustrated in FIGS. 10A and 10B.

FIG. 10A shows the line sensor charge accumulation control areas (Larea, C area and R area) when the amount of defocus is small (smalldefocus amount) and the subject images phase difference (that is, theextent of the displacement between the images) is also small. In thecase of a small defocus amount, the phase difference between the subjectimages is small and the breadth of each area can be narrowed, thusenabling focus state detection of a plurality of subjects from signalsobtained from each of these areas.

By contrast, FIG. 10B shows the line sensor charge accumulation controlarea (W area) when the amount of defocus is large (large defocusamount). The subject images phase difference is large, and therefore itis necessary to use the entire line as a single area in order to preventthe subject image from projecting beyond the boundaries of the area.

Thus, as described above, where the focus state detection apparatus ofJapanese Patent Application Laid-Open No. 63-172206 is adapted to themulti-point focus detection apparatus like the focus state detectionapparatus of Japanese Patent Application Laid-Open No. 2003-215442,initially a charge accumulation operation is carried out over a dividedarea like those shown in FIG. 10A even when the amount of defocus islarge, and thereafter, if the defocus amount is in fact large, it isthen necessary to carry out the charge accumulation operation once againover an area like that shown in FIG. 10B. Consequently, the time neededfor focus state detection necessarily lengthens, which is undesirable.

SUMMARY OF THE INVENTION

The present invention has been made in consideration of the abovesituation, and has as its object to provide a multi-point focusdetection apparatus that reduces the time needed for focus statedetection even when the amount of defocus is large.

According to the present invention, the foregoing object is attained byproviding a focus state detection apparatus comprising: a sensor thatsenses light rays that pass through a lens subjected to focus detectionand is composed of a plurality of photoelectric converter elements; acharge accumulation unit that accumulates pixel signals obtained by thesensor; a first accumulation controller that controls accumulationcarried out by the charge accumulation unit at each area of a pluralityof areas into which the sensor is divided; a second accumulationcontroller that combines at least a portion of the plurality of areasinto a single combined area and controls accumulation carried out by thecharge accumulation unit at such combined area; a first storage unitthat stores each accumulated signal of each of the plurality of areasaccumulation-controlled by the first accumulation controller; a secondstorage unit that stores the accumulated signal of the combined areaaccumulation-controlled by the second accumulation controller; and adefocus state detector that detects a defocus state of the area from theaccumulated signal stored in either the first storage unit or the secondstorage unit.

Other features, objects and advantages of the present invention will beapparent from the following description when taken in conjunction withthe accompanying drawings, in which like reference characters designatethe same or similar parts throughout the figures thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of the specification, illustrate embodiments of the invention and,together with the description, serve to explain the principles of theinvention.

FIG. 1 is a block diagram showing a circuit structure of a cameraaccording to an embodiment of the present invention;

FIG. 2 is a diagram showing an optical system layout of a cameraaccording to the embodiment of the present invention;

FIG. 3 is a diagram showing the optical structure of a phase differencefocus detection method-type focus state detection apparatus installed ina camera according to the embodiment of the present invention;

FIG. 4 is a diagram showing sensor arrays (line sensors) of a phasedifference focus detection method-type AF sensor according to theembodiment of the present invention;

FIG. 5 is a diagram showing the positional relation between distancemeasurement points and an AF field of view according to the embodimentof the present invention;

FIG. 6 is a block diagram showing the structure of an AF sensoraccording to the embodiment of the present invention;

FIG. 7 is a diagram showing an example of the pixel structure of the AFsensor according to the embodiment of the present invention;

FIG. 8 is a diagram illustrating a PB signal level and chargeaccumulation time control method according to the embodiment of thepresent invention;

FIG. 9 is a flow chart illustrating the operation of the focus statedetection apparatus according to the embodiment of the presentinvention; and

FIGS. 10A and 10B are diagrams illustrating focus state detectionmethods when the defocus amount is small and when the defocus amount islarge, respectively, in the conventional art as well as in the presentinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A preferred embodiment of the present invention will now be described indetail in accordance with the accompanying drawings.

FIG. 1 is a block diagram showing the circuit structure for a cameraaccording to an embodiment of the present invention. In FIG. 1,reference numeral 10 designates a camera microcomputer (hereinafter“CPU”) 100. A signal input circuit 204 for detecting the settings of agroup of switches 214 used for various operations of the camera, animage sensor 206, an AE sensor 207, a shutter control circuit 208 forcontrolling shutter magnets 218 a, 218 b, and an AF sensor 101 areconnected to the CPU 100. The CPU 100 exchanges signals 215 with animage sensing lens to be described later via a lens communicationscircuit 205 as well as controls a focus position and an aperture. Theoperations of the camera are determined by the settings of the group ofswitches 214.

The AF sensor 101 is provided with a pair of line sensors. Bycontrolling the AF sensor 101, the CPU 100 detects the amount of defocusfrom the contrast distribution of the subject obtained by the linesensors and controls the focus position of the image sensing lens.Moreover, by controlling the AE sensor 207, the CPU 100 detects thebrightness of the subject and determines the image sensing lens aperturesetting and shutter speed. Then, through the lens communications circuit205, the CPU 100 adjusts the aperture setting in the image sensing lens.In addition, through the shutter control circuit 208, the CPU 100controls the time the shutter magnets 218 a, 218 b are energized andthus adjusts the shutter speed, and further, controls the image sensor206 to carry out an image sensing operation.

Storage circuits 209 such as a ROM storing a program that controls theoperation of the camera, a RAM for storing variables, and an EEPROM(Electrically Erasable Programmable Read-Only Memory) for storing suchparameters are built into the CPU 100.

Next, a description will be given of the layout of the camera opticalsystem using FIG. 2.

Most of the light rays reflected from the subject entering the camerathrough an image sensing lens 300 are reflected upward by a quick returnmirror 305 and focused on a viewfinder screen 303. A user of the cameraobserves this image through a pentaprism 301 and an eye piece lens 302.A portion of the image sensing light rays passes through the quickreturn mirror 305 and is bent downward by a rear sub-mirror 306, througha field mask 307, a field lens 311, an aperture 308, and a secondaryfocusing lens 309, and focused on the AF sensor 101. By processing animage signal obtained by photoelectric conversion of this image, thefocus state of the image sensing lens 300 can be detected. During imagesensing, the quick return mirror 305 pops up, all the light rays arefocused on the image sensor 206, and exposure of the subject image iscarried out.

The focus state detection apparatus of the present embodiment, in FIG.2, is comprised of from the field mask 307 to the secondary focus mirror309 including the AF sensor 101. The focus state detection method ofthis focus state detection apparatus is the well known phase differencefocus detection method, enabling detection of the focus state of aplurality of different areas within the screen.

The detailed structure of the optical system for focus state detectionis show in FIG. 3. Light rays from the subject that pass through theimage sensing lens 300 are reflected by the sub-mirror 306 (see FIG. 2)and temporarily focused on the vicinity of the field mask 307 in aconjugated plane with an image sensing plane. In FIG. 3, paths of lightreflected back by the sub-mirror 306 are developed and shown. The fieldmask 307 is a member for shutting out extraneous light from points otherthan the distance measurement points (focus state detection area) in thescreen.

The field lens 311 causes the openings of the aperture 308 to focus onthe vicinity of the exit pupil of the image sensing lens 300. Thesecondary focusing lens is located behind the apertures 308 and iscomposed of a pair of lenses, with each lens corresponding to eachopening in the aperture 308. The light rays that pass through the fieldmask 307, field lens 311, the aperture 308 and the secondary focusinglens 309 are focused on the line sensors (sensor array) of the AF sensor101. Moreover, the line sensors of the AF sensor 101 are configured soas to be able to focus light rays from different subjects within theimage sensing screen as well.

A description will now be given of the relative positions of the linesensors on the AF sensor 101 and the distance measurement points in theimage sensing screen, with reference to FIG. 4 and FIG. 5.

FIG. 4 is a diagram showing the layout of the line sensors in the AFsensor 101. A pair of line-shaped line sensors 11 a and 11 b is disposedin the AF sensor 101.

FIG. 5 is a diagram showing the layout of the distance measurementpoints displayed in a viewfinder 500 and the range of an AF field 510 ofthe line sensors 111 a, 111 b on the AF sensor 101. Three distancemeasurement points L, C and R are set on the AF field 510, enablingfocus state detection for three different subjects corresponding to eachof the distance measurement points.

A description will now be given of the detailed circuit structure of theAF sensor 101, using the block diagram shown in FIG. 6.

The subject image focused by the secondary focusing lens 309 describedabove is photoelectrically converted at the line sensors 111 a, 111 b.The line sensors 111 a, 111 b are composed of a plurality of pixelsaligned in lines, with signals photoelectrically converted into voltagesat the pixels accumulated in charge accumulation circuits 102 a, 102 b.An area selection circuit 103 divides the signals accumulated in theaccumulation circuit 102 a among three areas and inputs the accumulatedsignals to PB contrast detection circuits 104 a, 104 b, 104 c.Furthermore, the area selection circuit 103 has the function to inputall the signals accumulated in the accumulation circuit 102 a and to aPB contrast detection circuits 104 d.

The PB contrast detection circuits 104 a, 104 b, 104 c and 104 d detectthe largest signals (hereinafter “Peak signals”) and the smallestsignals (hereinafter “Bottom signals”) among the accumulated signals ofthe pixels and outputs differential signals between the Peak signals andthe Bottom signals (hereinafter “PB signals”) to a charge accumulationcontrol circuit 105. The PB signals that are detected by the PB contrastdetection circuits 104 a, 104 b, 104 c and 104 d are called PB1, PB2,PB3 and PB4, respectively.

The charge accumulation control circuit 105 compares the PB1, PB2, PB3and PB4 to a target value. Then, when the PB1, PB2, PB3 and PB4 becomegreater than the target value, the charge accumulation control circuit105 outputs send signals to the charge accumulation circuits 102 a, 102b in order to send the accumulated signals corresponding to the rangesselected by the area selection circuit 103 to frame memories to bedescribed later. The accumulated signals of the areas that are input tothe PB contrast detection circuits 104 a, 104 b, 104 c are sent to firstframe memories 106 a, 106 b. Furthermore, the accumulated signal of allareas that is input to the PB contrast detection circuit 104 d is sentto second frame memories 107 a, 107 b, thus permitting simultaneouscharge accumulation control even if the areas to be subjected to chargeaccumulation control overlap. It should be noted that the first framememories 106 a, 106 b and the second frame memories 107 a, 107 b are notlimited to frame memories, provided that they have sufficient capacityto store the accumulated signals output from the charge accumulationcircuits 102 a, 102 b.

Once the signals of all the areas selected by area selection circuit 103are transmitted to the frame memories 106 a, 106 b, 107 a and 107 b, thecharge accumulation control circuit 105 causes the charge accumulationcircuits 102 a, 102 b to finish accumulation and to output anaccumulation finished signal to the CPU 100.

The accumulated signals stored in the first frame memories 106 a, 106 band the second frame memories 107 a, 107 b are output as accumulatedsignals at each pixel by the CPU 100 driving a shift register 108 to anoutput circuit 109. The output circuit 109 amplifies and otherwiseprocesses the accumulated signals and outputs the processed accumulatedsignals to an AD converter, not shown, of the CPU 100.

Using FIGS. 7 and 8, a description will now be given of an example inwhich the line sensors 111 a, 111 b are divided into three areas.

In FIG. 7, the line sensors 111 a and 111 b are each composed of 120pixels. An accumulated signal of a first pixel of line sensors 111 a isdesignated SA1 and an accumulated signal of an nth pixel is designatedSAn. Similarly, an accumulated signal of a first pixel of line sensor111 b is designated SB1 and an accumulated signal of an nth pixel isdesignated SBn.

Here, the area selection circuit 103 selects (assigns) areas such thatthe accumulated signals of the range of areas SA1-SA40 are input to PBcontrast detection circuit 104 a and the accumulated signals of therange of areas SA41-SA80 are input to PB contrast detection circuit 104b. In addition, area selection circuit 103 selects (assigns) areas suchthat the accumulated signals of the range of areas SA81-SA120 are inputto PB contrast detection circuit 104 c and the accumulated signals ofthe range of areas SA1-SA120 are input to PB contrast detection circuit104 d.

FIG. 8 is a diagram showing the relation between charge accumulationtime and the signal level of the PB signals PB1, PB2, PB3 PB4, which arethe output signals of the PB contrast detection circuits 104 a, 104 b,104 c and 104 d. A charge accumulation time 0 designates the start ofcharge accumulation, with the PB signals increasing as time passes.These signals are compared to an accumulation stop level by the chargeaccumulation control circuit 105. Times at which the PB signals PB1, PB2and PB3 meet or exceed the stop level are designated T1, T2 and T3,respectively. In such cases, at a time T1 the accumulated signalscorresponding to areas SA1-SA40 and SB1-SB40 input to the PB contrastdetection circuit 104 a are sent to the first frame memories 106 a, 106b. At a time T2, the accumulated signals corresponding to areasSA41-SA80 and SB41-SB80 input to the PB contrast detection circuit 104 bare sent to the first frame memories 106 a, 106 b. At a time T3, theaccumulated signals corresponding to areas SA81-SA120 and SB81-SB120input to the PB contrast detection circuit 104 c are sent to the firstframe memories 106 a, 106 b.

In addition, a time at which PB signal PB4 of the PB contrast detectioncircuit 104 d meets or exceeds the accumulation stop level is designatedT4. At time T4, an accumulated signal corresponding to all areasSA1-SA120 and SB1-SB120 input to the PB contrast detection circuit 104 dis sent to the second frame memories 107 a, 107 b.

The charge accumulation circuits 102 a, 102 b are configured so as to beable to send accumulated signals to the frame memoriesnon-destructively. For example, even after accumulated signal SA1-SA40and SB1-SB40 are sent to the first frame memories 106 a-106 b the chargeaccumulation operation is continued without destruction of thoseaccumulated signals. Therefore, at time T4, the accumulated signalscorresponding to all areas SA1-SA120 and SB1-SB120, including also theaccumulated signals of areas SA1-SA40 and SB1-SB40, can be sent to thesecond frame memories 107 a, 107 b. Accordingly, a re-accumulation ofthe signals for the purpose of sending them to the second frame memories107 a, 107 b is rendered unnecessary.

Thus, as described above, the PB signals that express subject imagecontrast are detected at each selected area and the signals areaccumulated until they meet or exceed a predetermined level, enablingoptimum charge accumulation control to be carried out at each area.

A detailed description will now be given of the operation of the focusstate detection apparatus configured as described above, based on theflow chart shown in FIG. 9.

Once a focus state detection start signal is received through operationof the group of switches 214, the AF sensor 101 starts focus statedetection. First, in step S710, the CPU 100 determines whether or notthe group of switches 214 is set to a large defocus mode or not. If thegroup 214 is set to the large defocus mode, processing then proceeds tostep S702 and a second charge accumulation control area capable ofdetecting a large amount of defocus, is set. By contrast, if the group214 is not set to the large defocus mode, processing then proceeds tostep S703 and a first charge accumulation control area is set.

A description will now be given of the first charge accumulation controlarea setting and the second charge accumulation control area setting,using FIGS. 10A and 10B.

FIG. 10A is a diagram illustrating a first charge accumulation controlarea set when the amount of defocus is small. As shown in FIG. 10A, theline sensors are divided into three parts, L area, C area and R area.The amount of defocus is small, and therefore the subject images do notproject beyond their respective areas and charge accumulation control isperformed at each area. As a result, it is possible to detect the focusstates of three different subjects. The area selection circuit 103within the AF sensor 101 is set to input the accumulated signals of thepixels of the L area to the PB contrast detection circuit 104 a, as wellas to input the accumulated signals of the pixels of the C area to thePB contrast detection circuit 104 b and the accumulated signals of thepixels of the R area to the PB contrast detection circuit 104 c,respectively. Moreover, although the line sensors are divided into threeareas when setting the first charge accumulation control area asdescribed above, the inputting of the accumulated signals of the W areato the PB contrast detection circuit 104 d is not carried out since inthis case there is no need to detect a large amount of defocus.Therefore, power to a W area of the PB contrast detection circuit 104 das well as to the second frame memories 107 a, 107 b for storing theaccumulated signals of the pixels of the W area is turned off to preventunnecessary power consumption.

FIG. 10B is a diagram illustrating the second charge accumulationcontrol area set when the amount of defocus is large. Examination of thebright C area in which a main subject is located indicates that thesubject image at this time projects beyond the C area. Accordingly, insuch an instance, the L area, C area and R area are combined into asingle W area, which enables the line sensors as a whole to obtain asingle continuous subject image signal, and enables detection of a focusstate in which the amount of defocus is large and the subject imagephase difference is large. The area selection circuit 103 is set so asto input the accumulated signals of the pixels of the W area to the PBcontrast detection circuit 104 d.

Returning to the flow chart shown in FIG. 9, in step S704 the CPU 100controls the AF sensor 101 and carries out charge accumulation controlfor the charge accumulation control areas set in either step S702 orstep S703 described above. Then, in step S705, the CPU 100 carries outdetection of a charge accumulation finished signal output from the AFsensor 101. The detection operation of step S705 is repeated unit theaccumulation finished signal is detected. Once the accumulation finishedsignal is detected, processing proceeds to a signal read operation ofstep S706.

When processing proceeds to step S706, the operation of reading thepixel signals of the areas is carried out. The CPU 100 controls the AFsensor 101 so as to cause the accumulated signals stored in the firstframe memories 106 a-106 b and the second frame memories 107 a, 107 b tobe output in succession, and the accumulated signals are AD converted byan AD converter in the CPU 100, not shown. Here, the AD-convertedaccumulated signals are stored in the storage circuits 209 in the CPU100. Next, in step S707, a correlation calculation is carried out on thebasis of the accumulated signals of the L area, C area, R area and Warea stored in the storage circuits 209 and the amount of defocus ineach of these areas is calculated. In other words, focus state detectionresults corresponding to each of an L distance measurement point of theL area, a C distance measurement point of the C area and an R distancemeasurement points of the R area are obtained. Moreover, in the largedefocus mode, when the amount of defocus is large, neither L area, Carea nor R area can be detected, and therefore results corresponding toa C distance measurement point are obtained from the W area.

Next, in step S708, the CPU controls the driving of the focus lens ofthe image sensing lens 300 through the lens communications circuit 205based on the amount of defocus calculated in step S707 and terminatesthe focus state detection operation sequence.

Thus, as described above, by providing the first frame memories 106 a,106 b that store accumulated signals when the amount of defocus is smalland the second frame memories 107 a, 107 b that stores accumulatedsignals when the amount of defocus is large, the present inventionsimultaneously enables the line sensors 111 a, 111 b to be divided intoa plurality of areas and charge accumulation control to be carried outat each area as well as enables charge accumulation control for a singlewide area composed of the plurality of areas combined. Therefore, when aplurality of subjects is present within the image sensing screen, it ispossible to carry out focus state detection for each subject. Moreover,although the amount of defocus might increase depending on the state ofthe image sensing lens and the position of the subject, in that case aswell, the time required for focus state detection can be reduced and therelease time lag shortened.

In addition, the PB signal that expresses subject image contrast isdetected at each selected area and stored until that signal meets orexceeds a predetermined level, enabling optimum charge accumulationcontrol for each area to be carried out.

In addition, in a case in which it is not necessary to carry outdetection when the amount of defocus is large, such as when it isapparent that the maximum amount of defocus is small, the presentinvention enables needless power consumption to be prevented byprohibiting charge accumulation control over a wide area composed of aplurality of areas combined and furthermore by cutting off the supply ofpower to those circuits related to charge accumulation control for suchwide area (specifically, the PB contrast detection circuit 104 d and thesecond frame memories 107 a, 107 b).

It should be noted that, although the charge accumulation area isdivided into three areas in the embodiment described above, the presentinvention is not limited thereto and charge accumulation control may bedivided among four or more areas. In such an instance, the focus statedetection apparatus may be configured so that it is possible to select amedium amount of defocus in addition to the large amount of defocus andthe small amount of defocus described above, such that, for example, twoof the four areas are combined and accumulation control is carried outover at least two or more areas combined.

As many apparently widely different embodiments of the present inventioncan be made without departing from the spirit and scope thereof, it isto be understood that the invention is not limited to specificembodiments thereof except as defined in the appended claims.

This application claims the benefit of Japanese Patent Application No.2005-031278 filed on Feb. 8, 2005, which is hereby incorporated byreference herein in its entirety.

1. (canceled)
 2. A focus state detection apparatus comprising: a sensorthat senses light rays that pass through a lens subjected to focusdetection and is composed of a plurality of photoelectric converterelements; an accumulation controller that selectively controlsaccumulation of pixel signals obtained by said sensor at each area of aplurality of areas into which said sensor is divided or at each combinedarea obtained by combining at least a portion of the plurality of areas;a first storage unit that stores each accumulated signal of each of theplurality of areas accumulation-controlled by said accumulationcontroller; a second storage unit that stores each accumulated signal ofeach of the combined areas accumulation-controlled by said accumulationcontroller; and a defocus state detector that detects a defocus statefrom the accumulated signals stored in said first storage unit and saidsecond storage unit.
 3. The focus state detecting apparatus according toclaim 2, wherein a charge accumulation unit continues a chargeaccumulation operation without erasing the accumulated signal even afterforwarding the accumulated signal to said first storage unit.
 4. Thefocus state detection apparatus according to claim 2, wherein: saidaccumulation controller individually compares a difference between amaximum signal and a minimum signal of the accumulated signals obtainedat each of the plurality of areas to a pre-set signal level, andindividually stops the accumulation operation at each area in which thedifference reaches the pre-set signal level, and compares a differencebetween a maximum signal and a minimum signal of the accumulated signalsobtained at the combined areas to a pre-set signal level, and stops theaccumulation operation when the difference reaches the pre-set signallevel.
 5. The focus state detection apparatus according to claim 2,wherein: said sensor is a pair of sensors each of which senses adifferent pair of light rays from among the light rays that pass throughthe lens; and said defocus state detector detects a defocus state basedon a phase difference obtained from the accumulated signals of a pair ofimages subjected to focus state detection focused on said sensor.
 6. Thefocus state detection apparatus according to claim 2, further comprisinga selection unit that selects a large defocus mode, wherein said defocusstate detector detecting a defocus state using an accumulated signalstored in said first storage unit when the large focus mode is notselected, said defocus state detector detecting a defocus state using anaccumulated signal stored in said second storage unit when the largefocus mode is selected.
 7. The focus state detection apparatus accordingto claim 2, wherein power to said accumulation controller and saidsecond storage unit is cut off when defocus state detection is carriedout using the accumulated signal stored in said first storage unit. 8.An optical instrument equipped with the focus state detection apparatusaccording to claim 2.